In an attempt to provide a colored film of high practicality, the inventor of the present invention has previously proposed a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, the pigment dispersion composition being adapted to fill micropores of the oxide film with a pigment by electrophoresis for coloration thereof, wherein a 50%-cumulative point (average particle diameter: D50) of the pigment particle diameter distribution in the dispersion is 200 nm or smaller. This pigment dispersion composition provides for a vivid color film having excellent weatherability and fastness and enables repetitive coloration because pigment particles are filled in the micropores of the aluminum oxide film to a great depth.
In actual use, however, the pigment is unavoidably deposited on the film surface as well as in the micropores when the electrophoresis is performed to fill the pigment into the micropores. The pigment deposited on the film surface other than in the micropores is likely to lead to an unstable color density of a thus colored material and to be brought into an electrodeposition surface coating bath in the succeeding step to contaminate the bath. With an anodic aluminum oxide film having micropores of diameters of about 50 nm or smaller, in particular, this tendency becomes more remarkable since most of the pigment is deposited on the film surface other than in the micropores, though depending on the size of the pigment particles. Even with an anodic aluminum oxide film having micropores of diameters of greater than 50 nm, the pigment is unavoidably deposited on the film surface as well as in the micropores, as stated above.
Thus, it has been required to wash away the pigment deposited on the film surface other than in the micropores irrespective of the micropore diameter of the anodic aluminum oxide film for convenience in the operational procedure in order to prevent such disadvantages. Typical means for washing away the pigment deposited on the film surface other than in the micropores are brushing, showering and like means which require cumbersome operations with time and labor. Therefore, the deposited pigment is preferably removed by simple immersion in still water or running water.
It is an object of the present invention to provide a pigment dispersion composition for fill-in coloration of an aluminum or aluminum alloy oxide film, which is adapted to fill pigment particles into micropores of the film to a great depth to provide for a vivid color film having excellent weatherability and fastness and allows repetitive coloration, and which permits the pigment deposited on the film surface other than in the micropores to be readily washed away by simple immersion in still water or running water.